Most canoes I've paddled have some flotation built into them, typically in the bow and stern. It would keep the boat afloat in the event it's capsized. Unless that's not already built into your canoe, I can't imagine why additional would be necessary.

I am not going to be in L Superior much, & I would think the inland lake swell would generally be less high & hazardous.

Yep, smaller lakes, smaller fetch, smaller waves. That said, several of the lakes are large enough to get choppy (and a little rough to paddle) and Siskiwit can get rolling enough that you might want to hole up and wait for it to calm when you are with a canoe.

Next, what are my best safety signaling protections ?
My radio transmits at 1,3, or 6 watts.
Your commenting on only a 5 mile range limit seems very limiting. Wondering if what use the radio is for inland lakes.
Do you know, does the IR Ranger station receive distress calls ?

If you're bringing a Marine VHF for safety, your best bet is to leave it on Channel 16, at 6 watts. IF an emergency arises, you will be set to do your best to try to contact help, but it may be of limited use inland. You should be prepared to be on your own and get yourself out of trouble. It could take a long time for help to arrive, especially considering it's a water emergency. Certainly wear a PFD, and work yourself to a shore. Know your general whereabouts, and the direction that could get you to an established trail.

Lake Ritchie canoe is around a mile or so (as the crow flies) west of the Lake Ritche campground.

Canoe flotation device: while this is up to you, you really should be prepared to be able to self rescue anywhere on ISRO. Depending on how you will be getting to the chain of inland lakes -- paddling down Rock Harbor to Moskey Basin and then portaging in or being dropped off at McCargoe or Chippewa Harbor and portaging in -- you may need flotation devices for your canoe. Lake Siskiwit can be very challenging and a flotation device will be necessary. Any time you are on Lake Superior (or a body of water connected to Lake Superior), a flotation device is needed.

Safety signaling: a VHF radio is a necessary safety device. 3-5 miles may get you to a passing boat on Lake Superior, even from an interior lake. The park rangers do have antennas on the fire towers which will extend line of sight significantly. The secondary safety signalling device to have is a ResQLink or similar device.

The park rangers do have the capability to receive distress calls. Keep in mind that, especially in the interior part of the island, you may be several hours or longer from outside assistance. In a true life/death situation, the Canadian Coast Guard can have a helicopter to ISRO in around an hour or so; The US Coast Guard has an air station in Traverse City, around 180 miles from ISRO as the helicopter flies, for evacuations. Per the 2017 Greenstone, the Malone Bay backcountry ranger station will be closed this summer. Again, the ability to self rescue cannot be understated. The Greenstone contains warnings about this -- heed them.

VHF reliability is all about line of sight. Most power boat radios are typically 25 watts but their biggest advantage not the extra power but their antenna is higher. Just that several extra feet can increase the range by several miles. The line of sight when both radios are 6 feet above the ground is just 3 miles. The park and most private boats monitor the marine emergency channel 16. The fairly tall land based antenna on Mott Island gives them most of their extra range. The old fire towers have repeater transmitters for use on their private VHF channels but I do not know if marine channel 16 is repeated. A handheld marine radio can be useless in many situations or it might save your life. It is also very handy for receiving the NOAA weather reports.

Other signalling devices you should carry are an audible one and a visual one. This can be as simple as a loud whistle and some flares. A small canister compressed air horn carries a long distance. There are also very small battery powered strobe lights that clip on to your PFD. All this, a sharp knife and some means to hopefully start a fire needs to be readily accessible to you in a floating container or bag should the worst happen.

Update:
I posed the question of monitoring marine emergency channel 16 on Isle Royale to the NPS. They did not directly answer my question as to whether any auto-repeating transmitters were in use, but I think the clear implication of their answer is no. Also, communication with Mott Island on Channel 16 would be "iffy". Here is their verbatim response:

Isle Royale Chief Ranger wrote:
The Windigo and Rock Harbor Ranger Stations monitor channel 16 regularly and you can hail them. You can try Mott, but we don't have a dedicated person near the radio like we do at the other ranger stations. There are almost always NPS vessels in Rock Harbor channel, so in an emergency, you can try hailing any NPS Ranger or any NPS vessel in addition to Rock Harbor Ranger Station.